Make vet happy on non_linux platforms. (#3549)

diff --git a/internal/syscall/syscall_nonlinux.go b/internal/syscall/syscall_nonlinux.go
index d3fd9da..ae0a911 100644
--- a/internal/syscall/syscall_nonlinux.go
+++ b/internal/syscall/syscall_nonlinux.go
@@ -18,6 +18,8 @@
  *
  */
 
+// Package syscall provides functionalities that grpc uses to get low-level
+// operating system stats/info.
 package syscall
 
 import (